For electronic equipment, small volume is a desirable attribute. Logic circuits have achieved small volume by being embodied in integrated circuits. However, achieving small volume for lumped elements such as resistors, capacitors, and inductors has proved more difficult, particularly for capacitors and inductors used at lower frequencies and higher currents. For many applications, capacitors of high capacitance values, such as those used for power supply and bypass filtering or low frequency coupling, are provided in the form of surface mounted packages.
A recent method for making small, high value surface mount capacitors is to use small strips of aluminum foil that are etched on both sides to have a very high surface area relative to a smooth surface. The etched aluminum strips are further processed by dipping processes that anodize the etched surfaces and coat the anodized surface with a conductive polymer. The anodizing forms a very thin dielectric, and the conductive polymer forms an opposing “plate” of the capacitor. The capacitors are then packaged by combining them in parallel, electrically, adding terminal leads, and molding into surface mountable packages. Such capacitors can have capacitances up to 100,000 times greater than conventional ceramic filled polymer embedded capacitors.
Such capacitors allow electronic equipment of reduced volume, but capacitors that occupy even less surface area of a printed circuit board are desirable.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.